Clinical Evaluation After Peripheral Nerve Repair With Caprolactone Neurotube

Natural polysaccharides and their derivatives as potential medical materials and drug delivery systems for the treatment of peripheral nerve injuries

Peripheral nerve repair following injury is one of the most serious problems in neurosurgery. Clinical outcomes are often unsatisfactory and associated with a huge socioeconomic burden. Several studies have revealed the great potential of biodegradable polysaccharides for improving nerve regeneration. We review here the promising therapeutic strategies involving different types of polysaccharides and their bio-active composites for promoting nerve regeneration. Within this context, polysaccharide materials widely used for nerve repair in different forms are highlighted, including nerve guidance conduits, hydrogels, nanofibers and films. While nerve guidance conduits and hydrogels were used as main structural scaffolds, the other forms including nanofibers and films were generally used as additional supporting materials. We also discuss the issues of ease of therapeutic implementation, drug release properties and therapeutic outcomes, together with potential future directions of research.

Peripheral Nerve Regeneration: Opportunities and Challenges

Peripheral nerve injury has detrimental effects on the quality of life for patients and is a worldwide issue with high rates of morbidity. Research on the molecular mechanisms of nerve injury, microsurgical techniques, and advances in stem cell research have led to substantial progress in the field of translational neurophysiology. Current research on peripheral nerve regeneration aims to accelerate peripheral nerve development through pluripotent stem cells and potential use of smart exosomes, pharmacological agents, and bioengineering of nerve conduits. In this article critically reviewed and summarized various methods used for peripheral nerve regeneration and highlight the opportunities and challenges that come along with these strategies.

Biomimetic Approaches for Separated Regeneration of Sensory and Motor Fibers in Amputee People: Necessary Conditions for Functional Integration of Sensory-Motor Prostheses With the Peripheral Nerves

The regenerative capacity of the peripheral nervous system after an injury is limited, and a complete function is not recovered, mainly due to the loss of nerve tissue after the injury that causes a separation between the nerve ends and to the disorganized and intermingled growth of sensory and motor nerve fibers that cause erroneous reinnervations. Even though the development of biomaterials is a very promising field, today no significant results have been achieved. In this work, we study not only the characteristics that should have the support that will allow the growth of nerve fibers, but also the molecular profile necessary for a specific guidance. To do this, we carried out an exhaustive study of the molecular profile present during the regeneration of the sensory and motor fibers separately, as well as of the effect obtained by the administration and inhibition of different factors involved in the regeneration. In addition, we offer a complete design of the ideal characteristics of a biomaterial, which allows the growth of the sensory and motor neurons in a differentiated way, indicating (1) size and characteristics of the material; (2) necessity to act at the microlevel, on small groups of neurons; (3) combination of molecules and specific substrates; and (4) temporal profile of those molecules expression throughout the regeneration process. The importance of the design we offer is that it respects the complexity and characteristics of the regeneration process; it indicates the appropriate temporal conditions of molecular expression, in order to obtain a synergistic effect; it takes into account the importance of considering the process at the group of neuron level; and it gives an answer to the main limitations in the current studies.

Preliminary results of posterior contralateral cervical 7 nerve transposition in the treatment of upper limb plegia after a stroke

OBJECTIVE

This study aimed to explore a shorter and safer contralateral C7 transposition pathway for the treatment of central upper limb paralysis.

METHODS

From July 2018 to March 2019, 10 patients with central upper limb paralysis underwent posterior cervical 7 nerve transposition. The age of these patients ranged within 31-58 years old (average: 44 years old). These patients comprised of eight male patients and two female patients. Nine patients had cerebral hemorrhage, and one patient had a cerebral infarction. Furthermore, nine patients presented with spastic paralysis of the upper limbs and one patient presented with nonspastic paralysis. The duration of plegia before the operation ranged from 6 to 60 months (average: 26 months). The surgical procedure included transposition of the contralateral cervical 7 nerve root via a posterior vertebral approach under general anesthesia, and the distal part of the contralateral cervical 7 nerve was anastomosed with the proximal part of the ipsilateral cervical 7 nerve.

RESULTS

The length of the contralateral cervical 7 nerve was 5.16 ± 0.21 cm, which was directly anastomosed with the ipsilateral cervical 7 nerve. Neither case needed nerve transplantation. Most patients had temporary numbness in their healthy fingers, which all disappeared within three months. Up to now, the follow-up results are as follows: The spasticity of the affected upper limbs in five patients is lower than that before the operation, the pain and temperature sensation of the affected upper limbs in six patients are better than before the operation.

CONCLUSION

The distance of nerve transposition can be shortened by a posterior vertebral approach operation, where the contralateral C7 nerve can be anastomosed directly with the ipsilateral C7 nerve which may be effective for nerve regeneration and functional recovery. However, this conclusion still needs further research and verification.

Modification of tubular chitosan-based peripheral nerve implants: applications for simple or more complex approaches

Surgical treatment of peripheral nerve injuries is still a major challenge in human clinic. Up to now, none of the well-developed microsurgical treatment options is able to guarantee a complete restoration of nerve function. This restriction is also effective for novel clinically approved artificial nerve guides. In this review, we compare surgical repair techniques primarily for digital nerve injuries reported with relatively high prevalence to be valuable attempts in clinical digital nerve repair and point out their advantages and shortcomings. We furthermore discuss the use of artificial nerve grafts with a focus on chitosan-based nerve guides, for which our own studies contributed to their approval for clinical use. In the second part of this review, very recent future perspectives for the enhancement of tubular (commonly hollow) nerve guides are discussed in terms of their clinical translatability and ability to form three-dimensional constructs that biomimick the natural nerve structure. This includes materials that have already shown their beneficial potential in in vivo studies like fibrous intraluminal guidance structures, hydrogels, growth factors, and approaches of cell transplantation. Additionally, we highlight upcoming future perspectives comprising co-application of stem cell secretome. From our overview, we conclude that already simple attempts are highly effective to increase the regeneration supporting properties of nerve guides in experimental studies. But for bringing nerve repair with bioartificial nerve grafts to the next level, e.g. repair of defects > 3 cm in human patients, more complex intraluminal guidance structures such as innovatively manufactured hydrogels and likely supplementation of stem cells or their secretome for therapeutic purposes may represent promising future perspectives.

The progress of biomaterials in peripheral nerve repair and regeneration

Repair and regeneration of the injured peripheral nerve (PN) is a challenging issue in clinics. Although the regeneration outcome of large PN defects is currently unsatisfactory, recently, the study of PN repair has considerably progressed. In particular, biomaterials for repairing PNs, such as nerve guidance conduits and nerve repair membranes, have been well developed. Herein, we summarize the anatomy of the PN, the pathophysiological features of the nerve injury, and the repair process post injury. Then, we highlight the progress in the development of natural and synthetic biomaterials and summarize the applications, advantages, and disadvantages of these materials. These materials can be used as nerve repair membranes and nerve conduits in the field of PN repair. Finally, we discuss the challenges encountered and development strategies for PN repair in the future.

Synthetic bioresorbable poly-α-hydroxyesters as peripheral nerve guidance conduits; a review of material properties, design strategies and their efficacy to date

Implantable tubular devices known as nerve guidance conduits (NGCs) have drawn considerable interest as an alternative to autografting in the repair of peripheral nerve injuries.

Nerve grafting for peripheral nerve injuries with extended defect sizes

Artificial and non-artificial nerve grafts are the gold standard in peripheral nerve reconstruction in cases with extensive loss of nerve tissue, particularly where a direct end-to-end suture or an autologous nerve graft is inauspicious. Different materials are marketed and approved by the US Food and Drug Administration (FDA) for peripheral nerve graft reconstruction. The most frequently used materials are collagen and poly(DL-lactide-ε-caprolactone). Only one human nerve allograft is listed for peripheral nerve reconstruction by the FDA. All marketed nerve grafts are able to demonstrate sufficient nerve regeneration over small distances not exceeding 3.0 cm. A key question in the field is whether nerve reconstruction on large defect lengths extending 4.0 cm or more is possible. This review gives a summary of current clinical and experimental approaches in peripheral nerve surgery using artificial and non-artificial nerve grafts in short and long distance nerve defects. Strategies to extend nerve graft lengths for long nerve defects, such as enhancing axonal regeneration, include the additional application of Schwann cells, mesenchymal stem cells or supporting co-factors like growth factors on defect sizes between 4.0 and 8.0 cm.

Scaffolds for peripheral nerve repair and reconstruction

Trauma-associated peripheral nerve defect is a widespread clinical problem. Autologous nerve grafting, the current gold standard technique for the treatment of peripheral nerve injury, has many internal disadvantages. Emerging studies showed that tissue engineered nerve graft is an effective substitute to autologous nerves. Tissue engineered nerve graft is generally composed of neural scaffolds and incorporating cells and molecules. A variety of biomaterials have been used to construct neural scaffolds, the main component of tissue engineered nerve graft. Synthetic polymers (e.g. silicone, polyglycolic acid, and poly(lactic-co-glycolic acid)) and natural materials (e.g. chitosan, silk fibroin, and extracellular matrix components) are commonly used along or together to build neural scaffolds. Many other materials, including the extracellular matrix, glass fabrics, ceramics, and metallic materials, have also been used to construct neural scaffolds. These biomaterials are fabricated to create specific structures and surface features. Seeding supporting cells and/or incorporating neurotrophic factors to neural scaffolds further improve restoration effects. Preliminary studies demonstrate that clinical applications of these neural scaffolds achieve satisfactory functional recovery. Therefore, tissue engineered nerve graft provides a good alternative to autologous nerve graft and represents a promising frontier in neural tissue engineering.

Partially oxidized polyvinyl alcohol conduitfor peripheral nerve regeneration

Surgical reconstruction of peripheral nerves injuries with wide substance-loss is still a challenge. Many studies focused on the development of artificial nerve conduits made of synthetic or biological materials but the ideal device has not yet been identified. Here, we manufactured a conduit for peripheral nerve regeneration using a novel biodegradable hydrogel we patented that is oxidized polyvinyl alcohol (OxPVA). Thus, its characteristics were compared with neat polyvinyl alcohol (PVA) and silk-fibroin (SF) conduits, through in vitro and in vivo analysis. Unlike SF, OxPVA and neat PVA scaffolds did not support SH-SY5Y adhesion and proliferation in vitro. After implantation in rat model of sciatic nerve transection, the three conduits sustained the regeneration of the injured nerve filling a gap of 5 mm in 12 weeks. Implanted animals showed a good gait recovery. Morphometric data related to the central portion of the explanted conduit interestingly highlighted a significantly better outcome for OxPVA scaffolds compared to PVA conduits in terms of axon density, also with respect to the autograft group. This study suggests the potential of our novel biomaterial for the development of conduits for clinical use in case of peripheral nerve lesions with substance loss.

PCL and PCL-based materials in biomedical applications

Biodegradable polymers have met with an increasing demand in medical usage over the last decades. One of such polymers is poly(ε-caprolactone) (PCL), which is a polyester that has been widely used in tissue engineering field for its availability, relatively inexpensive price and suitability for modification. Its chemical and biological properties, physicochemical state, degradability and mechanical strength can be adjusted, and therefore, it can be used under harsh mechanical, physical and chemical conditions without significant loss of its properties. Degradation time of PCL is quite long, thus it is used mainly in the replacement of hard tissues in the body where healing also takes an extended period of time. It is also used at load-bearing tissues of the body by enhancing its stiffness. However, due to its tailorability, use of PCL is not restricted to one type of tissue and it can be extended to engineering of soft tissues by decreasing its molecular weight and degradation time. This review outlines the basic properties of PCL, its composites, blends and copolymers. We report on various techniques for the production of different forms, and provide examples of medical applications such as tissue engineering and drug delivery systems covering the studies performed in the last decades.